Method of copper coating iron particles



Patented Sept. 27, 1949 METHOD or r 2,483,075 COPPER COATING IRONPARTICLES Edward C. Truesdale, Palmerton, Pa., assignor to The NewJersey Zinc Gompany, New York, N. Y., a corporation of New Jersey NoDrawing. Application December 15, 1944, Serial No. 568,397

3 Claims. (01. i17-100 This invention relates to cupreous-coated ironpowder for use in powder metallurgy, and has for its object theprovision of certain improvements in the manufacture of cupreous-coatediron powder.

As pointed out in the copending patent application of John L. Overholt,Ser. No. 563,396, filed December 15, 1944, cupreous-coated iron powdershave been found to possess certain advantageous properties for powdermetallurgical purposes. Thus, objects made of cupreous-coated ironpowder, compacted and sintered in accordance with drogen until reductionis complete, usually 1 to 2 hours. The resulting cupreous-co'ated ironparticles are cooled in an inert atmosphere (preferably hydrogen),milled lightly if necessary, and screened. Copper-coated iron powderswith a copper content of about 10% give excellent powder metallurgicalresults.

I have discovered that the inclusion of a small amount of copperchloride in themixture of iron powder and oxidized cupreous materialmaterially aids the complete envelopment of the iron parti cles in acontinuous coating of the reduced cupreous material. Based on thatdiscovery, the present invention involves the improvement in theaforementioned method of making cupreous-- coated iron powders whichcomprises including copper chloride, and preferably cuprous chloride, inthe mixture of iron powder and cuprous oxide or other oxidized cupreousmaterial. About by weight of the copper chloride, based on weight of themixture, gives excellent results, although marked improvement isattained with smaller amounts of copper chloride. The invention furthercontemplates the manufacture of cuprcous-coated iron particles by theinclusion in the mixture with iron powder of copper chloride, andpreferably cuprous chloride, as the sole or main source of copper. Whileeither cupric or cuprous chloride may be used in practicing theinvention, cuprous chloride is preferred since cupric chloride is toovolatile, hygroscopic and usually contains water of hydration. Thecopper chlorideshould be finely divided or pulverulent and preferablyanhydrous.

When iron powder and copper oxide are mixed in a mortar, by tumbling onpaper or in a ball mill, and regardless of the type of iron powder oroxide used, microscopical examination shows that the copper oxide doesnot uniformly coat the surface of the iron powder particles, but thatrelatively large areas are uncoated and the oxide tends to iiocculate;When such imperfectly coated iron particlesare reduced by hydrogen, thereduced copper migrates over the surface of the iron particles and moreor less completely envelopes them in a coating of copper, in spite ofthe fact that the temperature is too low for appreciable alloying tooccur, and that both iron and copper oxide are solids having noappreciable vapor pressure at the contemplated operating temperatures.Frequently, however, the coatings are poor, and many areas of theparticles are uncoated. This is particularly so when the iron powdercontains an appreciable amount of iron oxide, or when the copper oxideis made by roasting or oxidizingcopper (roasted copper oxide). .Theinclusion of copper chloride (preferably cuprous chloride) in themixture of iron powder and copper oxide promotes migration of thereduced copper over the surface ofthe iron particles resulting in morecomplete and satisfactory cupreous coating thereof.

7 It is believed that the copper chloride acts as aiiux or wettingagent, and so conditions or wets the surface of the iron particles thatthe reduced copper easily migrates over and completely envelopes them.Cuprous chloride melts at about 422 C. and experiments indicate that attemperatures of from 450 to 550 C. the melted cuprous chloride creepsover the surface of the iron particles before being itself reduced byhydrogen. Thus, the cuprous chloride wets the surface of the particlesand facilitates their envelopment by the reduced copper. It is alsopossible that the mutual solubility of cuprous oxide and cuprouschloride, and perhaps of iron oxide and cuprous chloride, aid inspreading the reduced copper over the iron particles. Whatever theexplanation, the presence of copper chloride during the hydrogenreduction of the mixed iron powder and copper oxide results in morecomplete and satisfactory coating of the iron particles by the reducedcopper, irrespective of the source and quality of the iron powder orcopper oxide or both.

The invention is particularly applicable to iron powders containing anappreciable amount of iron oxide. Thus, a poorly reduced, lowtemperature iron powder was mixed with electrolytic cuprous oxide (11.8C1120 based on the mixture) and reduced with hydrogen to obtain acoppercoated iron powder containing about 10% copper. The iron particleswere not completely coated, and many had substantial uncoated'surfaceareas. The addition of 1% cuprous chloride to a similar mixturecontaining 11.8% cuprous oxide, followed by hydrogen reduction undersimilar conditions, resulted in excellently coated iron particles withall surface areas covered.

The invention is also of particular advantage where the copper oxide orother oxidized cupreous material is made by roasting or oxidizingcopper. Thus, finely ball milled, roasted copper oxide (cuprous oxide)was elutriated with water to obtain a product of about 2 microns averageparticle size. A dispersing agent (sodium hexametaphosphate) was addedin order to obtain good size fractionation. The sized suspension wasthen flocculated, by the addition of a little sulphuric acid, to aidfiltration. The resulting pulverulent cuprous oxide was mixed with ahigh grade iron powder, and the mixture subjectedto hydrogen reductionto produce a copper-coated iron powder. The iron particles were notcompletely covered with the copper coating, and there were many uncoatedareas. The substitution of electrolytic copper oxide for the roastedcopper oxide resulted in somewhat better coated iron particles.Repetition-of these experiments with the addition of 1% by weight ofcuprous chloride to the mixtures of iron powder and cuprous oxide (11.8%by weight in each instance) resulted in greatly improved coatings, ofgood appearance and color and with few uncoated areas.

The use of hydrochloric acid instead of sulphuric acid as theflocculating agent during the filtration ofball-milled, roasted copperoxide results in the retention of some chloride (presumably cuprouschloride) by the copper oxide, and this is a suitable means forincorporating in the cuprous oxide some, if not all, of the copperchloride contemplated for the practice of the invention. Roasted copperoxide must be ball milled and elutriated to obtain the desired fineparticle size for cupreous coating. Similarly, electrolytic cuprousoxide may, and usually does, contain some chlorine, presumably ascuprous chloride. Thus, chlorine contents of from 0.6% to as much as1.5% have been found, by analysis, in various lots of commercialelectrolytic cuprous oxide. Such amounts of chlorine (as cuprouschloride) contribute beneficially to the 5 quality of the cupreouscoating, and this provides 4 another means for incorporating in cuprousoxide all or part of the desired cuprous chloride for the practice ofthe invention.

The cupreous coating on the particles of iron powder may be copperitself or it may be an alloy of copper such, for example, as bronze.Thus, in imparting a tinbronze coating to iron particles, the ironpowder is mixed with pulverulent cuprous oxide and stannic oxide, and inaccordance with the invention about 1% by weight of cuprous chloride isincluded in the mixture.

I claim:

l/In the method of coating with copper particles ol iron powder suitablefor use in powder metallurgy by subjecting an intimate mixture ofironpowder and a finely divided oxide of copper in the form of a coatingof the copper oxide on the particles of iron powder to a reducingtreatment with hydrogen, the improvement which comprises including about1% by weight of copper chloride in the mixture of iron powder and copperoxide. V M

2. In the method of imparting a cupreous coating to particles of ironpowder suitable for use in powder metallurgy in which the iron powder isintimately mixed with finely divided cuprous oxide to produce a coatingof the cuprous oxide on the particles of iron powder and the mixture issubjected to a, temperature of from 450 to 550 C. in an atmosphere ofhydrogen, the improvement which comprises including about 1% by weightof cuprous chloride in the mixture of iron powder and cuprous oxide. 7

3. The method of coating with copper particles of iron powder suitablefor use in powder metallurgy which comprises intimately mixing the ironpowder with finely divided cuprous oxide and about 1% by weight ofcuprous chloride to produce a coating of the oxide and chloride on theparticles of ironpowder, subjecting the mixture to a temperature of from450 to 550 C. in an atmosphere of hydrogen inthe course of which ironparticles are coated withreduced copper, and cooling the copper-coatedironrparticles in an inert atmosphere.

EDWARD C'. TRUESDALE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED- STATES PATENTS Number Name Date 1,587,637 Ferguson June 8, 19261,919,806 Schulz July 25, 1933

